What is the most important reason to create source cards

Your answer is - they include the information you will need to reference your material or locate it again. Gradpoint approved

is it "means of nourishment"

honestly you should not write it the word placement is not right and this does not sound right so i think you should write it this way. the life lessons i refused to learn, taught me the hard way this sounds way better you should try it! hope this is very !